Levulinic acid has been identified as a suitable chemical feedstock that may be processed from hexoses derived from biomass.
U.S. Pat. No. 2,813,900 discloses a process for continuous levulinic acid production. In this process the feed is biomass from which pentoses have first been recovered, more specifically the feed is a residue from a furfural process. The process is based on acid hydrolysis, wherein the cellulose polymers are degraded into hexose monomers in the first reactor, and reaction from hexoses to levulinic acid in second reactor, which is an elongated horizontally disposed chamber designed to create turbulence to the flow.
U.S. Pat. No. 5,608,105 discloses a process wherein carbohydrate feedstock and sulfuric acid catalyst solution are mixed, and the slurry is supplied continuously to a tubular reactor. This reactor is operated at an exemplary temperature of 210-220° C. in order to hydrolyse the carbohydrate polysaccharides into their soluble monomers (hexoses and pentoses). This hydrolysis reaction is rapid after which the outflow of the first reactor is fed to a continuously stirred tank reactor operated at a lower temperature (190-200° C.) with a longer residence time of 20 min. Levulinic acid is removed by drawing-off liquid from the second reactor. Solid by-products are removed from the levulinic acid solution in a filter-press unit.
Various processes for furfural production have been suggested. When aiming at low investment and low operating costs, production may be based on organic acids formed from biomass intrinsically by heating. Such a process is relatively slow and for example, allows furfural recovery only. To further develop the effectiveness and speed up the conversion, an acid catalyst may be added to the process to replace or act together with naturally occurring organic acids.
US Patent Publication No. US2013/0168227 discloses a process for furfural production from biomass, such as corn cob, bagasse and bamboo. In this method, initially biomass, acid catalyst, sulfolane as a water miscible solvent, and water were fed into the reactor. The furfural formed together with water, forming an azeotropic mixture, were distilled off leaving the solvent and residual side products, such as levulinic acid in the reactor. Humins and lignin which are soluble in sulfolane, were precipitated by addition of water and separated from side products.
Hence, there is a need to simplify the process of levulinic acid production. Another need is to convert biomass into levulinic acid and furfural in a more effective way. There is a further need to optimize the yield of both levulinic acid and furfural as reaction products. A combined process for conversion of hexoses and pentoses to levulinic acid and furfural respectively is therefore disclosed. Exemplary embodiments can improve both levulinic acid and furfural recovery in the process.